Semiconductor die such as diodes, transistors and the like are commonly processed (formed) simultaneously in a large area wafer. Such wafers may be made of monocrystaline silicon or other materials, such as gallium nitride on a suitable substrate such as silicon or the like.
Plasma etching equipment is used extensively in the processing of these substrates to produce semi-conductor devices. Such equipment typically includes a vacuum chamber fitted with a high density plasma source such as an Inductively Coupled Plasma (ICP) which is used to ensure high etch rates, necessary for cost-effective manufacturing. In order to remove the heat generated during the processing, the wafer (substrate) is typically clamped to a cooled support. A cooling gas (typically Helium) is maintained between the substrate and the support to provide a thermal conductance path for heat removal. A mechanical clamping mechanism, in which a downward force is applied to the top side of the substrate, may be used, though this may cause contamination due to the contact between the clamp and the substrate. More frequently an electrostatic chuck (ESC) is used to provide the clamping force.
After the processing steps are completed, the wafers are singulated, separating the die from the wafer. This “dicing,” separation or singulating operation is commonly carried out by sawing through the “streets” between the die within the wafers. Singulating the die of the wafer, for example, by sawing the wafer along the streets after the wafer is complete, including metal layers on the back or front side, can be a time consuming and costly process. Further, the singulation process can damage portions of the die, including the sides of the die.
Because of the potential damage, additional spacing is required between the dice on the wafer to prevent damage to the integrated circuits, e.g., the chips and cracks are maintained at a suitable distance from the actual integrated circuits so that the defects do not impair circuit performance or reliability. As a result of the spacing requirements, not as many dice can be formed on a standard sized wafer and wafer area that could otherwise be used for circuitry is wasted. The use of a saw exacerbates the loss of real estate on a semiconductor wafer. The blade of the saw is approximately fifteen microns thick. As such, to insure that cracking and other damage surrounding the cut made by the saw does not harm the integrated circuits, approximately one to five hundred microns of separation is typically maintained between the circuitry of each of the dice. Furthermore, after cutting, the dice require substantial cleaning to remove particles and other contaminants that result from the sawing process.
In an effort to overcome the disadvantages of sawing and scribing, chemical etching has been considered as an alternative for die singulation. Two methods of separating die by chemical etching are wet etching and plasma etching. Wet chemical etching techniques require an etch mask to be formed on at least one side of the wafer and, in some embodiments, both sides of the wafer. The etch mask defines where the substrate will be etched and protects the integrated circuits from the etchant. Once the mask is in place, the wafer is to be immersed in a wet etchant such as potassium hydroxide in the case silicon substrates. The wet etchant removes the substrate material from between the dice such that the dice are separated from one another. In the case of a silicon substrate, a wet etch technique is capable of removing silicon at a rate of about thirty microns per hour. Thus, even a wafer that has been thinned to a thickness of about two hundred microns will require about seven hours to complete the dicing process. Furthermore, there are well-known disadvantages to wet etch techniques such as the trenches formed with a wet etch do not have substantially vertical sidewalls, the trenches are relatively wide and, to achieve deep vertically directed trenches, the semiconductor wafer can only have certain specific crystal orientations. Additionally, some materials, such as GaN, can be difficult to wet etch with high enough rates to be economically feasible in a manufacturing process. Therefore, there is a need in the art for a method and apparatus for dicing a semiconductor wafer using a smaller separation between the dice and a fast dicing process.
Recently plasma etching techniques have been proposed as a means of separating die and overcoming some of these limitations. After device fabrication, the substrate is masked with a suitable mask material, leaving open areas between the die. The masked substrate is then processed using a reactive-gas plasma which etches the substrate material exposed between the die. The plasma etching of the substrate may proceed partially or completely through the substrate. In the case of a partial plasma etch, the die are separated by a subsequent cleaving step, leaving the individual die separated. The plasma etching technique offers a number of benefits over mechanical dicing:                1) Breakage and chipping is reduced;        2) The kerf or street dimensions between die can be reduced to well below twenty microns;        3) Processing time does not increase significantly as the number of die increases;        4) Processing time is reduced for thinner wafers; and        5) Die topology is not limited to a rectilinear format.        
For wafers that have back side metallization, die singulation is more complex. Back metal wafer dicing can be done with conventional sawing techniques though lower saw speeds and more frequent blade changes are required. Back metal dicing represents a bigger challenge for plasma etching techniques. Plasma etching systems are material dependent such that systems that are capable to etch through semiconductor materials like silicon, gallium arsenide, and sapphire, are not typically capable of etching through metals or metal alloys—particularly metals typically used in back metal stacks (e.g., gold, silver, copper and nickel). Hence, a plasma system that can etch wafers for dicing is may not be well suited to etch metals or metal alloys, thus a second etching tool may be required. To add further complexity to back metal dry etching, plasma etching through metals typically has a very narrow process window with the complications of potential for sputtering of the etched metal onto the side of the newly singulated die which may ultimately compromise device performance or reliability. Furthermore, it may be possible to etch the back metal prior to plasma etching the street regions. While this approach would avoid metal byproduct re-deposition on the singulated die walls, it represents an additional etch step that would require an aligned mask patterns on the back of the wafer.
Nothing in the prior art provides the benefits attendant with the present invention.
Therefore, it is an object of the present invention to provide an improvement which overcomes the inadequacies of the prior art devices and which is a significant contribution to the advancement to the dicing of semiconductor substrates using a plasma etching apparatus.
Another object of the present invention is to provide a method for dicing a substrate with back metal, the method comprising: providing the substrate having a first surface and a second surface, said second surface being opposed to said first surface, a mask layer on said first surface of the substrate, a thin film layer on said second surface of the substrate; dicing said first surface of the substrate through said mask layer to expose said thin film layer on said second surface of the substrate; and applying a fluid from a fluid jet to said thin film layer on said second surface of the substrate after said thin film layer has been exposed by the dicing step.
Yet another object of the present invention is to provide a method for dicing a substrate with back metal, the method comprising: providing a process chamber having a wall; providing a plasma source adjacent to the wall of the process chamber; providing a substrate support within the process chamber; providing the substrate having a first surface and a second surface, said second surface being opposed to said first surface, a mask layer on said first surface of the substrate, a thin film layer on said second surface of the substrate; placing the substrate onto said substrate support; generating a plasma using the plasma source; etching said first surface of the substrate through said mask layer using the generated plasma, the etching step exposing said thin film layer on said second surface of the substrate; and applying a fluid from a fluid jet to said thin film layer on said second surface of the substrate after said thin film layer has been exposed by the etching step.
Still yet another object of the present invention is to provide a method for dicing a substrate, the method comprising: providing a process chamber having a wall; providing a plasma source adjacent to the wall of the process chamber; providing a work piece support within the process chamber; providing the substrate having a first surface and a second surface, said second surface being opposed to said first surface, a mask layer on said first surface of the substrate, and a thin film layer on said second surface of the substrate; placing a work piece onto said work piece support, said work piece having a support film, a frame and the substrate; generating a plasma using the plasma source; etching said first surface of the substrate through said mask layer using the generated plasma, the etching step exposing said thin film layer on said second surface of the substrate; and applying a fluid from a fluid jet to said thin film layer on said second surface of the substrate after said thin film layer has been exposed by the etching step.
The foregoing has outlined some of the pertinent objects of the present invention. These objects should be construed to be merely illustrative of some of the more prominent features and applications of the intended invention. Many other beneficial results can be attained by applying the disclosed invention in a different manner or modifying the invention within the scope of the disclosure. Accordingly, other objects and a fuller understanding of the invention may be had by referring to the summary of the invention and the detailed description of the preferred embodiment in addition to the scope of the invention defined by the claims taken in conjunction with the accompanying drawings.